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This is a time of revolutionary change in the lighting industry. Solid-state lighting (SSL) systems are on track to achieve lighting efficacies for general lighting in excess of 150 lumens per watt (lm/W) in the not-too-distant future. This is double the typical performance of the ubiquitous linear fluorescent systems in use in commercial spaces today, and 10x the efficacy of the familiar incandescent light bulb, which many countries have regulated out of use in many applications in recent years. The total system performance could be further improved by the addition of smart controls, which include occupancy sensing and daylight harvesting, among other features.

Lighting quality is contextual, being a function of meeting the functions of the space (here expressed as individual well-being of people in buildings), while taking into account the economic and environmental context and the physical setting (here expressed as architectural considerations). Credit: (1).

These advances could mean that very soon, lighting designers and specifiers need not concern themselves with reducing lighting energy use, because the technologies will ensure that electric lighting is on only when needed, and uses as little energy as possible when it is on. At that point, the critical choices will be to put the right light in the right place to meet the goals for that installation. We will be able to focus on making the best use of light to achieve our goals.

In the late 1990s, the National Research Council of Canada (NRC) developed a model of lighting quality (1) that has since been adopted by the Illuminating Engineering Society of North America, the International Association of Lighting Designers, and the American Lighting Association. Lighting quality sits at the intersection of meeting individual needs, the economic and environmental context, and the architectural considerations (Figure above). Although developed with people and buildings in mind, the general approach is equally applicable for any installation: the individual well-being needs of people in buildings are analogous to the requirements for plant photosynthesis in greenhouses, or the ecological requirements of animals and birds in areas that are subject to sky glow. Thus, achieving good lighting quality is inherently sustainable, because it means addressing energy and environmental considerations – providing for the needs of future generations – while meeting the needs of the present.

When the SSL and smart lighting revolution is more fully developed, it will be more important than ever to know what lighting conditions will best meet the needs of the present. Energy use will not differentiate lighting choices, but understanding the lighting conditions that will suit the physical context and the needs of the users in the space will make it possible to choose the right equipment for the job. Fortunately, lighting researchers have been studying these questions for many years (at NRC since 1977), and most recently have turned their attention to the new features that smart controls and SSL systems provide.

Demonstrating the Value of Lighting Quality

“Is quality lighting worth the investment?” is a question frequently asked. Those asking the question are often faced with a decision to spend more to install equipment and controls that are said to save more energy or to promise a better environment for occupants. NRC researchers can answer this questions with a resounding “Yes” following a systematic 15-year path from tightly-controlled laboratory experiments (2, 3) to a semi-realistic office simulation (4) to longitudinal field studies (5, 6). We found that when people are able to work in conditions that broadly match their personal preferences, they judge the lighting to be of higher quality and the office to be more attractive; these people tend to be in a more positive mood, to be more focused on their work, and to show better well-being at the end of the workday (7). The field investigations found that being in lighting one judges as better also leads to fewer health problems and greater job satisfaction and organizational commitment. Thus, working in higher-quality lighting is good for individuals but also for their employers: it benefits organizational productivity both by facilitating work focus and by reducing costs for such thing as time off and employee turnover.

Our work also has shown that there are considerable individual differences in light level preferences in offices, meaning that the best way to ensure that people are able to experience their preferred light level is to provide a degree of individual control. On average, individual control over light level reduces energy use by ~10% over the typical fixed light level provided, because although some people desire a higher level, many others choose a lower level. Other important features of high-quality lighting systems are access to a window, daylight, and electric lighting that is distributed in a direct-indirect way, with some of the light being reflected off the ceiling and surrounding surfaces.

Colour-Tuning for Preferred White Light

The scale model. Credit: National Research Council of Canada.

Fluorescent systems generally are limited to providing light level control, but there are SSL systems that also offer individuals the possibility to choose the spectrum of the light source by using a combination of light-emitting diodes (LEDs) with varying colour outputs together with a luminaire design to mix the outputs and controls to dim each LED separately. We believe that a properly designed colour-tuning system can deliver a desirable range of white light options that will enable individuals to achieve their preferred conditions and trigger the same set of desirable outcomes as has been observed with light level control. Like other research groups around the globe, we have turned our attention to this new technology.

LED choices made during the scale model experiment, plotted on the 1931 CIE chromaticity diagram. The yellow dotted lines mark the boundary of possible conditions with these 5 channels. For more detail, please see the full paper. Credit: (8)

We started experimental work with a scale model experiment in which we examined the range of colour temperature and spectral power distributions of participants’ preferred lighting conditions (8). Figure 2 shows the scale model, which was a realistic 1:6 model of an open-plan office. Participants viewed a set of five pre-set LED spectra and one fluorescent lamp, and judged the appearance of the model; then they had the opportunity to modify the lighting to choose their personal preferences. In this case they had five LED channels to independently vary: red, green, blue, warm white and cool white. As predicted, people chose a wide range of different spectra (Figure 3). We can express the central tendency as an average (the median correlated colour temperature [CCT] was ~ 4300 K), but as is clear from this chart, individuals differ widely from one another.

Just before lunch, in Session 2, all the participants reported having Pleasure scores at or just below the midpoint of the scale. Those who were given the opportunity to choose the light source spectrum showed a small increase in Pleasure that was steady for the afternoon, whereas those with no choice stayed steady where they were (9). Credit: National Research Council of Canada.

We now are working at full scale in an office mock-up that is part of the NRC lighting laboratories. When we began this work there were no commercially-available luminaires for general office lighting that offered the range of colour-tuning capabilities we needed for this experiment. We designed our own, and created a custom interface to allow individuals to choose a colour by moving a cursor over a colour chart. In our first experiment, with data collected in 2010, we found that most of the temporary office workers who participated were unfamiliar with the idea of choosing a light source spectrum. People used the colour-tuning controls much more frequently than is typical with light level controls. As expected, they chose a wide variety of spectra, and they all reported that they liked having the opportunity to make those choices. Importantly, we saw some evidence that people given colour-tuning control halfway through the day experienced an uptick in mood compared to those who did not have the opportunity (9).

Our present work builds on this to refine the interface and the range of choices people may make. By following the systematic path from laboratory experiments to field interventions, we expect to extend our earlier findings for light level control to colour-tuning control. Thus far the work on colour-tuning tells us that we are on the right track. There is a broad range of individual preference for light source spectrum, and it appears that being able to obtain this preference leads to a more pleasant mood. With more familiarity with these concepts, and with an interface that can more easily deliver the preferred conditions, we expect to demonstrate the value to individuals and their employers of this novel feature.

Smart Lighting Design, Smart Controls

The lighting layouts in many commercial buildings are established long before the occupancy is known, with the result being a grid of regularly-spaced luminaires without regard for specific tasks or purposes. One of our earliest field investigations found that by replacing such a design with a custom installation of workstation-specific luminaires, lighting energy use dropped by 42% because of the design alone (10) (both the old and new installations used T8 fluorescent lamps on electronic ballasts). Adding controls for daylight harvesting, occupancy, and individual dimming control resulted in a total reduction in lighting energy use of 69% over the original installation. Smart lighting is not just a technology, it is a thought process.

Moving to SSL systems and associated technologies brings opportunities for further savings. Not only are SSL systems becoming more efficient than the systems they replace, but sensor technology has improved and become less expensive. It is not uncommon for every LED luminaire to have its own on-board occupancy sensor. Another line of NRC research concerns the energy savings that might result from this increased occupancy detection capability, as it is well known that combined signals from multiple sensors increases accuracy considerably. With improved detection accuracy, the time-out period before lights turn off because no one is present could be reduced from the code maximum 30-minute period to perhaps as little as one minute. Our simulations lead us to estimate that such a change could save 30% of the energy used with the 30-min delay (11).

“Light that follows” can save energy by selectively increasing the light level only where people are. We do not yet know how satisfactory this might be to the person who experiences it. Credit: National Research Council of Canada.

Another control option, and one currently offered by some manufacturers, is a smart lighting feature under which only those lights in the neighbourhood of an individual are turned on while the individual moves through the space (for example, walking along a corridor). As the occupant moves, the set of luminaires that is on moves with them (Figure 5). A thought experiment with energy calculations showed us that such a system might consume 42% of the energy annually that would be consumed by a conventional corridor lighting scheme with all lights on during occupied hours. We have built a prototype system in another of our laboratories to study how people respond to “light that follows”. There are many usability questions associated with this concept, which to our knowledge no one has tested yet: How large ought the lit area to be, and how quickly need it move with the walker? How dim can we make the surrounding area, without creating discomfort or feelings of insecurity? Does the lighting influence how quickly people walk along the corridor? Results are expected later this year.

Evidence-Based Lighting

As the technological side of the smart lighting revolution unfolds, the importance of understanding how to use light to achieve the programmatic goals for the space increases. Lighting systems and their controls are on the verge of solving most of the problems of lighting energy use, but these technologies cannot themselves tell us where, when, and how much light to use to achieve the program goals for the installations, be they in the office and commercial spaces where most of the recent NRC research has focused, or in homes, schools, health care settings, roadways, or protected ecological zones. Recent years have seen a dramatic increase in the breadth and number of submissions to the principal scientific journals in lighting, meaning that researchers around the world have responded to the call. This is very promising, because there is too much to know for any one group to solve all of the puzzles. Ongoing, interdisciplinary research can provide the knowledge that industry, regulators, designers and every individual can use to guide lighting choices. Everyone wins in this approach: Individuals experience conditions that help them to achieve their goals; organizations and society reap benefits from their well-being; the environment benefits from responsible environmental practices; and, manufacturers are able to develop and deliver lighting systems that provide maximum value to users. When all of these conditions are met, then we will have truly smart lighting.

Acknowledgements

The work described here was sponsored financially and with in-kind support by organizations too numerous to list here, including government agencies in Canada and the USA, the lighting industry, and electrical utilities. Detailed acknowledgements are available in the articles cited below.

Jennifer Veitch (@JenniferVeitch1) is a Principal Research Officer in NRC Construction, where she has led research into the effects of indoor environment effects on health and behaviour since 1992. She is best known for her work on lighting quality and individual control in relation to energy consumption, work performance and occupant satisfaction. She is a Fellow of several associations in lighting and psychology. In 2011 she received the Waldram Gold Pin for Applied Illuminating Engineering from the International Commission on Illumination (CIE). She currently serves CIE as Director of its Division 3, Interior Environment and Lighting Design.